The present invention relates generally to voltage detectors and more particularly to a voltage detector suitable for use in an Armament Circuits Preload Test Set.
Armament Circuits Preload Test Sets, are used, for example, with air to air missiles, launchers, gravity and guided bombs, multi-ejector racks, and other munitions release systems on combat aircraft. Aircraft on which Armament Circuits Preload Test Sets are used include the F-15 fighter, models A, B, C, D, and E. Armament Circuits Preload Test Sets comprise a voltage detector and interface adapters. The interface adapters provide electrical connection between the voltage detector and various connector types located on the aircraft. The conventional voltage detector performs at least four key test functions when used in an Armament Circuits Preload Test series. The voltage detector assesses Presence of Voltage, continuity in an Electroexplosive Device (EED), and Stray Voltage. The voltage detector also performs an Adapter Test.
An EED conventionally consists of a conductor and a primary combustible material. A variety of propulsion systems and ordnance use an electrical signal to initiate combustion. This signal can be a dc current. Ohmic heating due to dc current flowing in the conductor can raise conductor temperature rapidly. Once a minimum ignition temperature of the primary combustible material is reached, the primary material ignites, which in turn initiates combustion of a secondary material. Part of the Armament Circuits Preload Tests may include a continuity check in an FED. The same conventional voltage detector performs an ohmic Adapter Test and two voltage tests.
The Stray Voltage Test determines whether a circuit that is in an unenergized state is actually free of any voltage that could cause a malfunction in the tested circuit. For example, an FED must normally be tested to ensure that the circuit is free of any stray voltages that could cause an improper triggering of the primary combustible material.
For the conventional voltage detector, an input voltage greater than 0.120 VDC or less than −0.120 VDC causes the voltage detector to turn on the indicator light. The conventional voltage detector comprises the attachment of a 3 ohm load resistance to the measurement circuit for the Stray Voltage Test.
The Presence of Voltage test determines whether an input voltage between 22.0 VDC and 47.0 VDC is present. In the conventional voltage detector, if an input voltage of less than 22.0 VDC is detected, then a test light turns off. Alternatively, however, if the measured input voltage is greater than 47.0 VDC, then a protection circuitry within the conventional voltage detector trips a protection fuse. Before the conventional voltage detector can make subsequent measurements, the fuse must be replaced. And the fuse is not readily accessible, requiring the removal of screws for removal and replacement. Therefore, a technician using the conventional voltage detector would need to have spare fuses at hand and deal with the additional duties of repairing the voltage detector before proceeding with an Armament Circuits Preload Test. Another alternative is to have multiple voltage detectors in each Armament Circuits Preload Test Set.
The conventional voltage detector can also trip the indicator light for a voltage level less than 22.0 VDC and can also invoke the protection circuit for voltages greater than 47.0 VDC. That is, adjustments can be made for measured-input voltage as low as 3.5 VDC to turn off the indicator light. Likewise, an over-voltage as high as 300 VDC can be measured before blowing the protective fuse.
External resistors are used to adjust the level for which the indicator light will turn off or for which the fuse will blow, under voltage and over voltage, respectively. The conventional analog voltage detector 100 and internal resistors circuit 110 is shown in FIG. 1a. The over voltage protection circuit of the conventional voltage detector is not shown.
External resistors are used to vary the input voltage level which trips under voltage or over voltage. For an under voltage trip point greater than 22.0 VDC, an external resistor 126 is connected in series with TEST_IN+ 120 to create a voltage divider between the external resistor and the internal 300 ohm load 112, as shown in FIG. 1b. Connection for TEST_IN+ measurement is moved to 121, in this configuration.
For an under voltage trip point of 3.5 VDC, the TRIP_ADJ pin 130 is connected to TEST_IN+ 120 via connector 122, as shown in FIG. 1c. This configuration raises the input voltage at sense input 142. For under voltage trips between 3.5 and 22 VDC, the TRIP_ADJ pin 130 is connected via connector 122 to TEST_IN+ 120 and an external resistor 126 is connected in series with TEST_IN+, moving the TEST_IN+ measuring point to position 121, as shown in FIG. 1d. Adjustments to raise the over voltage trip point above 47.0 volts before triggering the over protection circuit are not shown.
It would be desirable to have a voltage detector which is compatible with the Armament Circuits Preload Test Sets, which does not require fuse replacement upon sensing of over-voltage.